Field of the Invention
This invention is directed to substituted heterocyclic methane sulfonates as sacrificial agents in enhanced oil recovery.
In the recovery of oil from oil-bearing subterranean reservoirs, it usually is possible to recover only minor portions of the original oil in place by the so-called primary recovery methods which utilize only the natural forces in the reservoir. In order to increase the production of oil from subterranean reservoirs, resort has been taken to a variety of supplemental (secondary) recovery techniques. The most widely used supplemental technique is waterflooding, which involves the injection of water into the reservoir. As the water moves through the reservoir, it acts to displace oil therein toward a production system comprising one or more wells through which the oil is recovered.
It has long been recognized that factors such as the interfacial tension between the injected water and the reservoir oil, the relative mobilities of the reservoir oil and injected water, and the wettability characteristics of the rock surfaces within the reservoir are factors which influence the amount of oil recovered by waterflooding. Thus, it has been proposed to add surfactants to the flood water in order to lower the oil-water interfacial tension and/or to alter the wettability characteristics of the reservoir rock. Also, it has been proposed to add viscosifiers such as polymeric thickening agents to all or part of the injected water in order to increase the viscosity thereof, thus decreasing the mobility ratio between the injected water and oil and improving the sweep efficiency of the waterflood.
Surfactants used for enhanced oil recovery, particularly brine tolerant surfactants, are very expensive. Such surfactants tend to be absorbed by the rocks and clays in the reservoir, thus depleting their concentration in the waterflood fluid and diminishing their effectiveness by unfavorably increasing oil-water interfacial tension. A way to reduce absorptive loss is to use cheaper chemicals, i.e., sacrificial agents, that are absorbed on the rock, leaving the surfactants relatively less absorbed and free for its intended purpose.
The addition of various compounds to enhanced oil recovery fluids to reduce absorptive loss of surfactants to rock is not a new concept. Compounds which have been found to be effective include sodium phosphates (Roszelle U.S. Pat. No. 3,688,844), sodium silicates [P. Somasundaran and H. S. Hanna, Society of Petroleum Engineers, paper 7059 (1978] and lignosulfonates [Kalfoglou U.S. Pat. No. 4,000,779 and Anon., Paper Trade Journal, 163, 21 (1979)]. These compounds were selected for their cheapness and effectiveness. However, it has been found that certain low molecular weight heterocyclic methanesulfonates of the present invention are even more effective than the most effective of the above named compounds, namely, the lignosulfonates.